1. Field Of The Invention
The present invention relates to wiring devices in general, and more particularly to that type of device sometimes heretofore generally described as a solderless terminal, wherein a screw is advanced toward a seat for the purpose of exerting pressure effective to tightly clamp the stripped end of one or more conductor wires between a pressure plate constituted by the tang or connecting tab of a contact element and a seat provided in the terminal collar body or yoke. Such devices are usable to advantage in many types of wiring devices, as for example cord connectors of the type disclosed in co-pending application of James M. Wittes, Ser. No. 910,569 filed May 30, 1978. Terminal collars of the type disclosed herein are also usable to advantage in terminal blocks, bus bar assemblies, or indeed in any of a wide number of locations in which a conductor wire is to terminate and be electrically connected to a connection or terminal point.
2. Description Of The Prior Art
Terminal collars of the type disclosed are per se very well known. The most usual type is an integral, closed loop into which a screw is threaded, in which the loop is a slice of an elongated seamless tube. These have great strength and may be formed to a thickness sufficient to comply readily with UL standards as regards metal thickness and threads (UL Standard 498 as revised Mar. 24, 1978 provides that the metal shall be "at least 0.050 inch thick and shall have no fewer than 2 full threads in the metal for a terminal screw").
The disadvantage of such a terminal collar is, first of all, that it is expensive to make; and yet has the deficiency in that it does not maintain a tight clamping pressure on the wire conductor during the alternating cycles of heating and cooling of the wire, producing correspondingly alternating expansion and contraction cycles with resultant tendency toward loosening of the connection over a period of time.
A typical example of a terminal collar of the type disclosed above will be found in U.S. Pat. No. 3,775,733 (the modification shown in FIG. 6).
To overcome the deficiencies of terminal collars of the kind described immediately above, the prior art has developed terminal collars in which the clamping yokes are formed from simple, rectangular metal strips which may in and of themselves be of a thickness less than the prescribed UL Standard quoted above. In such instances, the strip metal blank is bent upon itself so that its end portions overlap, in the manner shown in FIG. 4 of the above-mentioned U.S. Pat. No. 3,775,733. In this type of device, the overlapping end portions are of a combined thickness that meets the UL Standard, and both end portions are tapped to provide the required number of threads. Such devices of this type, as heretofore made, nevertheless also have deficiencies in that force vectors exerted against the overlapping end portions during the clamping of a conductor in the yoke tend to misalign and damage the threads. Further, such devices as have heretofore been made, though designed for the purpose of maintaining clamping pressure during contraction and expansion cycles of the conductor, have nevertheless not been fully efficient in this regard. This is by reason of the fact that all of the clamping pressures are translated into the above-mentioned force vectors with the undesirable effect upon the threads noted. Or, separately or in addition to the tendency toward multilation of the threads, such devices have not heretofore been designed with sufficient elasticity to accommodate themselves to the contraction and expansion cycles of the wire conductor, except perhaps by transmission of all forces, that result from stressing of the metal, directly to the overlapping end portions of the metal strip without absorption or damping of said forces enroute to the threads formed in the overlapping end portions.